The present invention relates to a battery charging system for charging a battery by a generator driven by an engine, and more particularly to the charging system for charging the battery efficiently in the manner that the generator is controlled at a constant speed by feedback control and that the battery is adaptively charged in accordance with gases generated in the battery (hereinunder called as gassing).
There is recently proposed an electric vehicle having an electric motor as a driving source, which is developed to achieve low pollution without using petroleum fuel, or a hybrid motor vehicle in which an internal combustion engine is combined with the electric motor. In such a vehicle, battery conditions influence performance of the vehicle to determine the maximum mileage in dependency on a power capacity of the battery.
The vehicle needs a charging device for efficiently charging the batteries to improve the performance. For example, Japanese Issued Patent Publication No. 49-30648 (1974) discloses a charging device as the prior art of this invention.
In the prior art, the charging device comprises an internal combustion engine with a generator in order to charge the battery, a switching circuit connected to a power source, and both an ignition device and a starter connected to the source through the switching circuit for respectively igniting and starting the engine. The switching circuit actuates the ignition device and the starter when battery energy becomes lower than a predetermined level, and the circuit stops the starter when starting operation of the engine finishes. At the same time, the switching circuit stops to provide the power to the ignition device when engine load becomes lower than a predetermined value. As a result, charging efficiency of the battery is improved by driving the engine in a high-efficient region.
However, even though an engine speed is maintained at a fixed speed for driving the generator, a generator speed is not maintained at the same speed because of a power transmission loss due to slipping of a belt which connects the engine with the generator, so that it is difficult to precisely control the charging.
Namely, having the relation with load connected to the output, the output of the generator is not maintained in an optimum state even when the engine speed is maintained at the fixed speed. The conventional charging device has the problem that the engine speed must be changed to a proper speed corresponding to the battery condition in each occasion.
Furthermore, the battery mounted on the vehicle has a phenomenon that an amount of gases such as hydrogen (H.sub.2) and oxygen (O.sub.2) sharply increases at the end of charging. The phenomenon is called "gassing". Namely, most of the charging energy is consumed by the electrolysis of water, thereby wasting the power.
Gassing occurrence is detected only by human eye so that the battery charging efficiency and construction of an automatic charging system is not improved. The gassing occurrence causes the battery electrolyte to decrease rapidly, thereby shortening the battery life and resulting the possibility of fire by flammable gas.